nRF54L15 SPI corruption on GPIO2/P2 when RTT is disconnected

[ppk2]

Hi,

I'm working on a custom board with the nRF54L15 using NCS 3.2.1, and have configured spi21 on port 2 for a display.

SPI pin configuration:
SCK: P2.06 (TRACECLK)
CS: P2.07 (TRACEDATA[0] / SWO)
MOSI: P2.08 (TRACEDATA[1])
D/C: P2.10 (TRACEDATA[3])

I am seeing some strange behaviour; the SPI bus works perfectly as long as I have an active RTT session open/connected. As soon as I disconnect RTT the SPI signal becomes corrupted/noisy.

I suspect TIPU or SWO logic is claimin or driving these pins by default and that RTT is somehow suppressing them while connected.

I've tried the following config, but the issue persists:
CONFIG_DEBUG=n
CONFIG_TRACING=n
CONFIG_SEGGER_SYSTEMVIEW=n
CONFIG_CONSOLE_SUBSYS=n
CONFIG_CONSOLE_HANDLER=n

Is there a specific config,UICR setting or TAD register I need to clear to completely release port 2 for GPIO/SPI use?

Any help would be much appreciated.

[Vidar Berg]

Hi,

Since SPIM21 and P2 reside on different power domains, you can not allow the chip to enter the lowest power modes while the SPI is operating, please see Cross power-domain use and nRF54L pin mapping for details how you can handle this.

When starting an RTT session you are also enabling the debug interface mode on the chip which keeps these domains always powered, hence masking the problem.

Best regards,

Vidar